In the fields of displays for use in television receivers and information terminals, studies have been made for replacing conventionally mainstream cathode ray tubes (CRT) with flat-panel displays which are to comply with demands for a decrease in thickness, a decrease in weight, a larger screen and a high fineness. Such flat panel displays include a liquid crystal display (LCD), an electroluminescence display (ELD), a plasma display panel (PDP) and a cold cathode field emission display (FED). Of these, a liquid crystal display is widely used as a display for an information terminal. For applying the liquid crystal display to a floor-type television receiver, however, it still has problems to be solved concerning a higher brightness and an increase in size. In contrast, a cold cathode field emission display uses cold cathode field emission devices (to be sometimes referred to as “field emission device” hereinafter) capable of emitting electrons from a solid into a vacuum on the basis of a quantum tunnel effect without relying on thermal excitation, and it is of great interest from the viewpoints of a high brightness and a low power consumption.
FIGS. 33 and 34 shows a cold cathode field emission display to which the field emission devices are applied (to be sometimes referred to as “display” hereinafter). FIG. 33 is a schematic partial end view of the conventional display, and FIG. 34 is a schematic partial perspective view of the display when a cathode panel CP and an anode panel AP are disassembled.
The field emission device shown in FIG. 33 is a so-called Spindt-type field emission device having a conical electron emitting portion. Such a field emission device comprises a cathode electrode 111 formed on a supporting member 110, an insulating layer 112 formed on the supporting member 110 and the cathode electrode 111, a gate electrode 113 formed on the insulating layer 112, an opening portion 114 formed in the gate electrode 113 and the insulating layer 112 (a first opening portion 114A formed in the gate electrode 113 and a second opening portion 114B formed in the insulating layer 112), and a conical electron emitting portion 115A formed on the cathode electrode 111 positioned in the bottom portion of the second opening portion 114B. Generally, the cathode electrode 111 and the gate electrode 113 are formed in the form of a stripe each in directions in which the projection images of these two electrodes cross each other at right angles. Generally, a plurality of field emission devices are arranged in a region (corresponding to one pixel, and the region will be called an “overlapped region” or an “electron emitting region” hereinafter) where the projection images of the above two electrodes overlap. Further, generally, such electron emitting regions are arranged in the form of a two-dimensional matrix within an effective field (which works as an actual display portion) of a cathode panel CP.
An anode panel AP comprises a substrate 30, a phosphor layer 31 (31R, 31B and 31G) which is formed on the substrate 30 and has a predetermined pattern, and an anode electrode 33 formed thereon. One pixel is constituted of a group of the field emission devices formed in the overlapped region of the cathode electrode 111 and the gate electrode 113 on the cathode panel side and the phosphor layer 31 which is opposed to the above group of the field emission devices and is on the anode panel side. In the effective field, such pixels are arranged on the order of hundreds of thousands to several millions. On the substrate 30 between one phosphor layer 31 and another phosphor layer 31, a black matrix 32 is formed.
The anode panel AP and the cathode panel CP are arranged such that the electron emitting regions and the phosphor layers 31 are opposed to each other, and the anode panel AP and the cathode panel CP are bonded to each other in their circumferential portions through a frame 34, whereby the display is produced. In an ineffective field (ineffective field of the cathode panel CP in the example shown in the drawings) which surrounds the effective field and where a peripheral circuit for selecting pixels is formed, a through-hole 36 for vacuuming is provided, and a tip tube 37 is connected to the through-hole 36 and sealed after vacuuming. That is, a space surrounded by the anode panel AP, the cathode panel CP and the frame 34 is in a vacuum state.
A relatively negative voltage is applied to the cathode electrode 111 from an cathode-electrode control circuit 40, a relatively positive voltage is applied to the gate electrode 113 from a gate-electrode control circuit 41, and a positive voltage having a higher level than the voltage applied to the gate electrode 113 is applied to the anode electrode 33 from the anode-electrode control circuit 42. When such a display is used for displaying on its screen, a scanning signal is inputted to the cathode electrode 111 from the cathode-electrode control circuit 40, and a video signal is inputted to the gate electrode 113 from the gate-electrode control circuit 41. Due to an electric field generated when a voltage is applied between the cathode electrode 111 and the gate electrode 113, electrons are emitted from the electron emitting portion 115A on the basis of a quantum tunnel effect, and the electrons are attracted toward the anode electrode 33 and collide with the phosphor layer 31. As a result, the phosphor layer 31 is excited to emit light, and a desired image can be obtained. That is, the working of the display is controlled, in principle, by a voltage applied to the gate electrode 113 and a voltage applied to the electron emitting portion 115A through the cathode electrode 111.
The method of producing a Spindt-type field emission device will be explained below with reference to FIGS. 35A, 35B, 36A and 36B which are schematic end views of the supporting member 110 and the like constituting the cathode panel.
This method is in principle a method of forming the circular-cone-shaped electron emitting electrode 115A composed of a metal material by vertical vapor deposition. That is, vaporized particles perpendicularly enter the first opening portion 114A formed in the gate electrode 113. The amount of the vaporized particles which reach the bottom portion of the second opening portion 114B is gradually decreased by utilizing the shielding effect of an overhanging deposit formed around an opening edge portion of the first opening portion 114A, so that the electron emitting portion 115A as a circular-cone-shaped deposit is formed in a self-aligned manner. The method will be explained in which a peeling-off layer 116 is formed in advance on the insulating layer 112 and the gate electrode 113 for easing removal of an unnecessary overhanging deposit. In FIGS. 35A, 35B, 36A and 36B, only one electron emitting portion is illustrated.
[Step-10]
A conductive material layer composed, for example, of polysilicon for a cathode electrode is formed on a supporting member 110 composed, for example, of a glass substrate by a plasma-enhanced CVD method. Then, the conductive material layer for a cathode electrode is patterned by a lithographic method and a dry etching method, to form the cathode electrode 111 having a stripe form. Thereafter, an insulating layer 112 composed of SiO2 is formed on the entire surface by a CVD method.
[Step-20]
Then, the conductive material layer (for example, TiN layer) for a gate electrode is formed on the insulating layer 112 by a sputtering method. Then, the conductive material layer for a gate electrode is patterned by a lithographic method and a dry etching method, to form the stripe-shaped gate electrode 113. The cathode electrode 111 in the form of a stripe extends in a direction rightward and leftward to the paper surface of the drawing and the gate electrode 113 in the form of a stripe extends in a direction perpendicular to the paper surface of the drawing.
[Step-30]
Then, a resist layer is formed again, a first opening portion 114A is formed in the gate electrode 113 by etching and the second opening portion 114B is formed in the insulating layer 112 by etching, so as to expose the cathode electrode 111 in the bottom portion of the second opening portion 114B, and then, the resist layer is removed, whereby a structure shown in FIG. 35A can be obtained.
[Step-40]
As shown in FIG. 35B, a peeling-off layer 116 is then formed on the gate electrode 113 and the insulating layer 11 by oblique vapor deposition of nickel (Ni) while the supporting member 110 is turned. In this case, the incidence angle of vaporized particles relative to a normal of the supporting member 110 is set at a sufficiently large angle (for example, an incidence angle of 65° to 85°), whereby the peeling-off layer 116 can be formed on the insulating layer 112 and the gate electrode 113 almost without depositing any nickel in the bottom portion of the second opening portion 114B. The peeling-off layer 116 extends from the opening edge portion of the first opening portion 114A like eaves, whereby the diameter of the first opening portion 114A is substantially decreased.
[Step-50]
Then, an electrically conductive material such as molybdenum (Mo) is deposited on the entire surface by vertical vapor deposition (incidence angle 3° to 10°). During the above vapor deposition, as shown in FIG. 36A, as the conductive material layer 117 having an overhanging form grows on the peeling-off layer 116, the substantial diameter of the first opening portion 114A is gradually decreased, the vaporized particles which contributes to the deposition in the bottom portion of the second opening portion 114B gradually comes to be limited to particles which pass the central region of the first opening portion 114A. As a result, a circular-cone-shaped deposit is formed on the bottom portion of the second opening portion 114B, and the circular-cone-shaped deposit constitutes the electron emitting electrode 115A.
[Step-60]
Then, as shown in FIG. 36B, the peeling-off layer 116 is peeled off from the insulating layer 112 and the gate electrode 113 by a lift-off method, and the conductive material layer 117 above the insulating layer 112 and the gate electrode 113 is selectively removed. In this manner, a cathode panel CP having a plurality of the Spindt-type field emission devices can be obtained.
In the above display constitution, it is effective to sharpen the top end portion of the electron emitting portion for attaining a large current of emitted electrons at a low driving voltage, and from this viewpoint, the electron emitting portion 115A of the above Spindt-type field emission device can be said to have excellent performances. And, the above manufacturing method of a Spindt-type field emission device has an advantage that a circular-cone-shaped deposit can be formed as an electron emitting portion 115A in a self-aligned manner with regard to the opening portions 114A and 114B. However, the formation of the conical electron emitting portion 115A requires advanced processing techniques, and with an increase in the size of the display and with an increase in the area of the effective field, it is beginning to be difficult to form the electron emitting portions 115A uniformly all over the effective field since the number of the electron emitting portions 115A totals up to tens of millions in some cases.
There has been therefore proposed a so-called flat-type field emission device which uses a flat electron emitting portion exposed in a bottom portion of an opening portion without using the conical electron emitting portion. The electron emitting portion of the flat-type field emission device is formed on a cathode electrode positioned in the bottom portion of the opening portion, and it is composed of a material having a lower work function than a material constituting the cathode electrode for achieving a high current of emitted electrons even if the electron emitting portion is flat. In recent years, it has been proposed to use various types of carbon materials such as a carbon-nanotube as the above material.
In the manufacture of the above flat-type field emission device, a structure shown in FIG. 35A is obtained, and then a thick-film-paste-material layer 122 made, for example, of negative-type photosensitive paste containing carbon-nanotubes is formed on the entire surface including the inside of the opening portion 114 (see FIG. 37A). Then, the thick-film-paste-material layer 122 is exposed to exposure light (see FIG. 37B), further, followed by development, removal of an unnecessary portion of the thick-film-paste-material layer 122 and then firing of the remaining thick-film-paste-material layer 122, whereby an electron emitting portion 115 can be obtained (see FIG. 37C). Reference numeral 119 indicates an exposure mask.
Meanwhile, before the thick-film-paste-material layer 122 is exposed, the exposure mask 119 is aligned in relation to a reference marker (not shown) that is provided beforehand, so that the exposure mask 119 and the opening portion 114 are not out of position.
However, the supporting member 110 undergoes deformation, for example, due to a thermal history of the supporting member 110 or stresses of various layers (cathode electrode 111, insulating layer 112, gate electrode 113, etc.) formed on the supporting member 110. As a result, when the thick-film-paste-material layer 122 is exposed, an alignment failure actually takes place between the exposure mask 119 and the opening portion 114 in many places. When such a phenomenon occurs, the distance from the opening end portion of the first opening portion 114A formed in the gate electrode 113 to the electron emitting portion 115 positioned in the bottom portion of the second opening portion 114B varies, and as a result, the electron emissions from the electron emitting portions 115 vary, which causes display non-uniformity. In the worst case, part of the thick-film-paste-material layer 122 is left on the side wall of the opening portion 114, so that a short circuit is formed between the gate electrode 113 and the cathode electrode 111 by such a thick-film-paste-material layer 122.
One means that is thinkable to overcome the above problem is a method in which a resist-material layer 120 for covering the side wall of the opening portion 114, the gate electrode 113 and the insulating layer 112 is formed (see FIG. 38A) after the structure shown in FIG. 35A is obtained, a negative-type thick-film-paste-material layer 122 containing carbon-nanotubes is formed on the entire surface including the inside of the opening portion 114 (see FIG. 38B). In the above method, however, the resist-material layer 120 is dissolved by the thick-film-paste-material layer 122, which actually results in a state shown in FIG. 37A instead of bringing about a state shown in FIG. 38B, so that it is no longer significant to provide the resist-material layer 120.
Another method may be thinkable, in which a mask layer made of a material insusceptible to the thick-film-paste-material layer 122 is formed in place of the resist-material layer 120. That is, a mask layer made of a material insusceptible to the thick-film-paste-material layer 122 is formed on the entire surface including the inside of the opening portion 114, a resist layer is formed on the mask layer, an opening portion is formed through the resist layer positioned above the bottom portion of the opening portion, the mask layer is etched with using the resist layer as an etching mask, and then resist layer is removed, thereby to remove the mask layer from the bottom portion of the opening portion. However, this method is complicated and requires an additional cost.
It is therefore an object of the present invention to provide a method of patterning a thick-film-paste-material layer with a resist material without any problem, a method of manufacturing a cold cathode field emission device in which an electron emitting portion made of a thick-film-paste-material can be formed with a resist material without any problem, and a method of manufacturing a cold cathode field emission display, to which the above method of manufacturing a cold cathode field emission device is applied.